I believe that it is fair. If carbon credits are recognized which they are in the market then they should be legal and able to use them. If the global market starts to turn and shows signs of not using these credits anymore than I believe it would not be justified for these corporations to work to keep them in use.
This is actually a very clever way to make money, and it gives people incentive to rack up carbon credits. As a matter of fact, I may give this a try now that I know it is possible. Any extra revenue would help at the present time, and this is a great idea.
The rights to produce carbon by the ton are granted to certain companies. The government has a limited number of these carbon credits in order to limit our damage to the environment. The environment is not damaged any more or any less based on who or what emits this carbon. If the people want less carbon emitted, then less credits should be granted. If there is an excess of carbon credits available, then the amount granted can be reduced.
The idea of carbon credits came about as a way for companies and individuals to reduce greenhouse gases. The concept was a good one until some companies realized they had accumulated an excess of carbon credits from various projects and started selling the credits to other companies wanting to reduce their carbon footprint. I think this should not be allowed as it is not the purpose they were intended for.
It is not okay for corporations to make money buying and selling carbon credits. This is not a concrete product or service and I don't believe that making money on an abstract thing is ethical. Corporations are best suited to selling ideas on how to reduce carbon rather than trying to make money on something abstract.